The present invention pertains generally to industrial curtains and doors used as environmental closures for openings through which traffic can still pass. The curtains generally comprise a plurality of usually transparent strips that are suspended contiguously to each other from a hanger or support generally fixed adjacent to a top margin of the opening. Each of the strips usually consists of a length of flexible, generally transparent, material terminating adjacent to a lower margin of the opening. The present invention relates particularly to improvements that will provide enhanced margin visibility particularly in low light situations.
Strip curtains and doors are conventionally employed to provide closures between, for example, separate manufacturing areas within large buildings, warehouses and the like. Goods are often required to be transported from one area of a manufacturing or storage facility to another where one or the other of the areas is heated, air-conditioned or even refrigerated. On occasion, other environmental concerns need to be addressed such as dust, fumes, smoke, dirt, or even noise. Where the traffic is only occasional, conventional doors can be employed to close any doorway between the two areas. Where the traffic is considerable, the use of conventional doors gives way to suspended flexible screens or curtains, which inhibit the wholesale transfer of air from one area to the other yet still permit goods-transporting vehicles such as fork lifts to pass through with little effort.
The doors and curtains are generally made of elongated plastic strips that hang side-by-side from a support system mounted to extend across the top of the opening. For safety reasons, it is desirable that the curtain be sufficiently transparent that one operating a transporting vehicle be able to see any hazard or obstruction that might exist on an opposite side of a curtain before proceeding through. Persons on the opposite side of a curtain also desire to be able to see oncoming transport vehicles so appropriate evasive action can be taken. Thus, plastic materials, which were more or less transparent, such as polyvinyl chloride and polyethylene, were adopted as the preferred materials for forming such screens as shown, for example, in U.S. Pat. Nos. 4,095,642, 4,165,778, 4,232,725, 4,289,190, 4,607,678, 5,127,460, and 6,394,171.
U.S. Pat. No. 4,312,396 discloses that the strips forming such doors can be transparent, opaque, or in any desired color, depending on the expected use. As a practical matter, however, opaque strips running the full vertical length of a door inhibit the visibility needed by transportation vehicle operators and others as previously indicated. When used a doors, transportation equipment operators have found it desirable for some of the strips in strip curtain doors, such as the outer edge strips or a center divider strip, to be made of a contrasting or different color for delineating either the sides of the opening or the center of a passageway, or both as suggested by U.S. Pat. No. 4,257,471. This has typically been carried out by incorporation a tinting agent in the plastic forming the colored strips that only minimally reduces the transparency of the strips.
While such colored strips perform adequately in well lighted situations to identify the sides of a doorway opening, the differences in color become difficult to discern in low light situations. Further no attention has been paid to the overhead margin of the doorway opening, which can be quite important to vehicles that have a variable height requirement.